In http://docs.mongodb.org/manual/core/replica-set-sync/ a few sections can be updated for new storage engines.

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Is this true for all storage engines from the "Multithreaded Replication" section. If it is true then it limits my ability to have long running queries on a replica that isn't getting far behind on replication.

'While applying a batch, MongoDB blocks all reads. As a result, secondaries can never return data that reflects a state that never existed on the primary.'

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The "Prefetching Indexes" section is only true for mmapv1, which is explained in the docs for the referenced parameter, secondaryIndexPrefetch, but I think the docs here could be updated.